In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder or powder suspension referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly. In a slightly different arrangement, toner may be transferred to an intermediate surface, prior to retransfer to a final substrate.
Transfer of toner from the charge retentive surface to the final substrate is commonly accomplished electrostatically. A developed toner image is held on the charge retentive surface with electrostatic and mechanical forces. A substrate (such as a copy sheet) is brought into intimate contact with the surface, sandwiching the toner thereinbetween. An electrostatic transfer charging device, such as a corotron, applies a charge to the back side of the sheet, to attract the toner image to the sheet.
Unfortunately, the interface between the sheet and the charge retentive surface is not always optimal. Particularly with non-flat sheets, such as sheets that have already passed through a fixing operation such as heat and/or pressure fusing, or perforated sheets, or sheets that are brought into imperfect contact with the charge retentive surface, the contact between the sheet and the charge retentive surface may be non-uniform, characterized by gaps where contact has failed. There is a tendency for toner not to transfer across these gaps. A copy quality defect results.
That acoustic agitation or vibration of a surface can enhance toner release therefrom is known, as described by U.S. Pat. No. 4,111,546 to Maret, U.S. Pat. No. 4,684,242 to Schultz, U.S. Pat. No. 4,007,982 to Stange, U.S. Pat. No. 4,121,947 to Hemphill, Xerox Disclosure Journal "Floating Diaphragm Vacuum Shoe, by Hull et al., Vol. 2, No. 6, November/December 1977, U.S. Pat. No. 3,653,758 to Trimmer et al., U.S. Pat. No. 4,546,722 to Toda et al., U.S. Pat. No. 4,794,878 to Connors et al., U.S. Pat. No. 4,833,503 to Snelling, Japanese Published Patent Application 62-195685, U.S. Pat. No. 3,854,974 to Sato et al., and French patent No. 2,280,115.
Resonators for applying vibrational energy to some other member are known, for example in U.S. Pat. No. 4,363,992 to Holze, Jr., U.S. Pat. No. 3,113,225 to Kleesattel et al., U.S. Pat. No. 3,733,238 to Long et al., and U.S. Pat. No. 3,713,987 to Low.
Coupling of vibrational energy to a surface has been considered in Defensive Publication T893,001 by Fisler. U.S. Pat. No. 3,635,762 to Ott et al., U.S. Pat. No. 3,422,479 to Jeffee, U.S. Pat. No. 4,483,034 to Ensminger and U.S. Pat. No. 3,190,793 Starke.
Resonators coupled to the charge retentive surface of an electrophotographic device at various stations therein, for the purpose of enhancing the electrostatic function, are known, as in: U.S. Pat. No. 5,210,577 to Nowak; U.S. Pat. No. 5,030,999 to Lindblad et al.; U.S. Pat. No. 5,005,054, to Stokes et al.;; U.S. Pat. No. 5,010,369 to Nowak et al.; U.S. Pat. No. 5,025,291 to Nowak et al.; U.S. Pat. No. 5,016,055 to Pietrowski et al.; U.S. Pat. No. 5,081,500 to Snelling; U.S. Pat. No. 5,282,005 to Nowak, et al.; and U.S. Pat. No. 5,329,341 to Nowak, et al.
In the ultrasonic welding horn art, as exemplified by U.S. Pat. No. 4,363,992 to Holze, Jr., where blade-type welding horns are used for applying high frequency energy to surfaces, it is known that the provision of slots through the horn perpendicular to the direction in which the welding horn extends, reduces undesirable mechanical coupling of effects across the contacting horn surface. Accordingly, in such art, the contacting portion of the horn is maintained as a continuous surface, the horn portion is segmented into a plurality of segments, and the horn platform, support and piezoelectric driver elements are maintained as continuous members. For uniformity purposes, it is desirable to segment the horn so that each segment acts individually. However, a unitary construction is also highly desirable, for fabrication and mounting purposes.
It has been noted that even with fully segmented horns, as shown in U.S. Pat. No. 5,010,369 to W. Nowak, et al., there is a fall-off in response of the resonator at the outer edges of the device. A similar fall off is shown in U.S. Pat. No. 4,363,992 to Holze, Jr., at FIG. 2, showing the response of the resonator of FIG. 1.
Of interest is U.S. Pat. No. 4,826,703 to Kisler which suggests that in a coating apparatus controlled by variations in an electrode potential connected to a vibrator. U.S. Pat. No. 4,546,722 to Toda et al., U.S. Pat. No. 4,794,878 to Connors et al. and U.S. Pat. No. 4,833,503 to Snelling describe ultrasonic transducer-driven toner transfer for a development system, in which a vibration source provides a wave pattern to move or assist in movement of toner from a sump to a photoreceptor. U.S. Pat. No. 4,568,955 to Hosoya et al. teaches recording apparatus with a developing roller carrying developer to a recording electrode, and a signal source for propelling the developer from the developing roller to the recording media.
As exemplified by U.S. Pat. No. 4,363,992 to Holze, Jr., for blade-type welding horns, the horn is coupled with the transducer with a bolt type fastener. U.S. Pat. No. 3,113,225 to Kleesattel et al shows a similar arrangement for other ultrasonic energy applying applications. In the application proposed by the cross-referenced applications, for the release of toner from an image carrying surface, a bolted construction is problematic, as it requires extreme precision in the tightening of the bolts. Any variation of the clamping force will cause asymmetric device behavior, when uniform behavior is sought. The bolt torque can be controlled, but the axial compression cannot be easily controlled. The bolt to thread friction losses are a random bolt to bolt variable.
U.S. Pat. No. 4,713,572 to Bokowski, teaches the use of adhesive in adhering a horn to a piezoelectric element. In U.S. patent application Ser. No. 07/620,520, "Energy Transmitting Horn Bonded to an Ultrasonic Transducer for Improved Uniformity at the Horn Tip", by R. Stokes et al. teaches the use of an epoxy mesh which serves to bond a ceramic piezoelectric elements to the surface of the horn as well as provided electrical contact for the A.C. drive voltage to excite the element. The epoxy mesh behaves as a low pass mechanical filter, attenuating the transfer of energy from the active element to the waveguide. Variations in dimensions of the epoxy mesh, surface finish, and localized pressure during assembly process influence the coupling between the piezoelectric element and the waveguide resulting in nonuniform vibration amplitude across the process width.
A simple, relatively inexpensive and accurate approach to replace costly ceramic piezoelectric elements which are coupled to a horn and to improve the uniformity of vibration has been a goal in the design, and manufacture of such devices. This need has been particularly recognized in the ultrasonic energy applying applications used in electrophotographic printers. The need to provide accurate and inexpensive attachment of a horn to a piezoelectric element has become more acute, as the demand for high quality, electrophotographic printers has increased.